Help Please- pH solutions for enzyme pracs

[Ocean Breeze]

I need to make up pH solutions 1, 9, 11 & 13.

Its for a liver/catalase enzyme prac. But dont know what to use or how to make up these pH solutions.

Would be grateful for any help asap.

Thanks

[RosalieM]

this may sound crazy, but do a search for hydroxide and you will find some ways to get the exact pHs. If you search pH it is ignored, if you search solutions you get 35 pages! I was looking for it last week. Took me ages to come up with something but I knew they were there! There are a few different methods out there but I haven't tried them yet so I can't recommend any above any others.

[Ocker]

Hey Sky! for that prac just make up some buffer solutions from "The Laboratory" page 50
Keep the Faith!

[Krysia Lee]

For pH 1 mix 25mL 0.2M KCl with 48.5mL 0.2MHCl then make up to 100mL with distilled water.
pH 9 mix 25mL 0.2M boric acid with 29.5mL 0.5M borax make up to 100mL with distilled
pH 11 Solution A 2.4g anhydrous boric acid and 10.5g monohydrous citric acid make up to 1L. Solution B 19g tri-sodium phosphate,12 hydrate dissolved and made up to 500mL. ForpH 11 add 22mL solution A to 78mL solution B.
pH 13 Sorry I've got nothing

[fibreweb]

We did ours very simply with
HCl 0.05M which had a pH of about 2.42
HCl 0.01M Which had a pH of about 4.34
Our tap water was 7.8
NaOH 0.01M which had a pH of 9.03
NaOH 0.05 M which had a pH of 11.9

Whilst these are not the exact figures you asked for they did provide the range of pH that is required by the sylabus and were a whole lot easier and simpler to provide.

I am very lucky to have teachers that are not pedantic and finiky or want fancy and hard to get stuff

Wendy

[Ocean Breeze]

Thanks Ocker

Thanks for all this info and replies.
What would we do without each other

Go team
Go Network

[JelJane]

You might find this site helpful...
http://delloyd.50megs.com/moreinfo/buffers2.html
Cheers, Jane

[lada]

Do we really need a buffer solution for this practical, or would just the right pH solution do just as well? I have been preparing buffer solutions for years, takes a lot of time, when Kimmy suggested to do just pH solutions.
pH1 is 0.1M HCl
and then do 1:10 dilutions until pH6, pH7 distilled water
pH14 1M NaOH and again 1:10 dilutions until pH8.

I started doing this last year and teacher does not complain.

Lada

[Ocker]

Yes Lada! We all do that, but than you meet a teacher who doesn't really know and understand what they are doing, so they have to invent difficulties

[rae]

Interesting discussion about using buffers. I have always struggled with getting solutions with the right pH for this prac so this year decided to use preprepared buffers I had in the chem store. We used pH 4 and 10 and i think 7 with spinach and peroxide. The results were nothing like they should be. We then used 0.1M HCl and 0.01M HCl and the results were what we expected.
The we decideed that one of the chemical in the buffers interferred with the enzyme.

[Ocker]

That's interesting
Are you monitoring this Rainbow?

[sunray18]

I am monitoring! After the fuss this year with disc soaked in yeast.. back to the old potato one, where we soaked pieces of potato in the 3 prepared buffers and popped them into 1% peroxide.. worked a treat

[ana.santos]

Making PH Solutions

To Make 200ml of each solution

To make a 200ml solution of PH1 to PH7
PH1 = .1 mol HCL 220ml (Base Solution)
PH2 = 20 ml .1 mol HCL + 180ml distilled Water + 200ml = PH2
PH3 = 20 ml PH2 Solution + 180ml distilled Water + 200ml = PH3
PH4 = 20 ml PH3 Solution + 180ml distilled Water + 200ml = PH4
PH5 = 20 ml PH4 Solution + 180ml distilled Water + 200ml = PH5
PH6 = 20 ml PH5 Solution + 180ml distilled Water + 200ml = PH6
PH7 = Distilled water should have a PH of 7

To make a 200ml solution of PH14 to PH8
PH14 = 1.0 mol NaOH 220ml (Base Solution)
PH13 = 20ml NaOH + 180ml Distilled Water = 200ml PH13
PH12 = 20ml PH13 + 180ml Distilled Water = 200ml PH12
PH11 = 20ml PH12 + 180ml Distilled Water = 200ml PH11
PH10 = 20ml PH11 + 180ml Distilled Water = 200ml PH10
PH9 = 20ml PH10 + 180ml Distilled Water = 200ml PH9
PH8 = 20ml PH9 + 180ml Distilled Water = 200ml PH8
PH7 = Distilled water should have a PH of 7

Maybe this will help.

Cheers,
Ana

[kimmy]

we always do our pH the same as Ana and never have had a problem.

[Ocean Breeze]

yes I am here

Thanks everyone for all you help. This is SO helpful

[Rita]

We are doing this prac tomorrow. (Liver and pH).
Are you using specific pH solutions only to add to the liver OR do you adjust the Hydrogen peroxide pH using specific pH solutions?
I have been asked for pH adjusted Hydrogen Peroxide.
Slightly confused. Maybe it's because it is Monday.

[DavidPeterson]

I adjust the pH of the peroxide:

The Teacher/Lab Guide to our Year 12 Practical Book suggests (for 100mL of solution, scale up as needed):

pH1: 60mL of 6% peroxide + 40mL 2M HCl

pH3: To 60mL H2O2 add 38mL of distilled water. Test the pH. It will be approximately 5. Add HCL dropwise until pH is 3 and then make up to 100mL with water.

pH 6, 7, 8, 10: Take 10mL of 2M NaOH and make up to 100mL. Reserve thiss solution. Then take 60mL of peroxide and add 30mL water. Add the NaOH until required pHs are reached then make up to 100mL.

pH12: to 60mL of peroxide add 35mL of the diuted NaOH from before. Measure pH. if approx 12 then make up to 100mL. If not, add extra Naoh solution dropwise until approx 12 and make up to 100mL.

pH13: to 60mL peroxide add 40mL 2M NaOH.

Hope this works for you. I don't use this method - I'm a bit hit and miss. I start with the peroxide, measure the pH then add NaOH or HCl as required.

[Rita]

Thank you

[mtg]

There's another thread on this suggesting capsicum instead of liver. We tried it, works well and smells good.

[rae]

We always struggle with this prac. I found the following method in an old post.( Thanks to Whspa) I did this yesterday and it worked brilliantly and was super easy to set up.

Pepsin is an enzyme which aids in the breakdown of proteins and is secreted in the stomach of most
animals. It functions at a very low pH, which makes it ideal to use for studying the effect of pH on
enzyme activity. Commercial or natural albumin can be used as the protein source; however hardboiled
egg white is more impressive to demonstrate the action of pepsin.

Materials
Egg white (hard-boiled)
Test tubes (6)
Test tube rack
Solutions:
A: 1.0% Pepsin
B: Pepsin (1.0%) in 0.4% hydrochloric acid
C: 0.4% Hydrochloric acid
D: Pepsin (1.0%) in 0.5% sodium bicarbonate
E: 0.5% Sodium bicarbonate
F: Distilled water
Metric ruler
Knife

Procedure
1. Label test tubes A to F.
2. Fill each tube 1/3 full (5 ml) with the corresponding solution.
3. Drop a small (2 mm) cube of egg white into each tube.
4. Incubate at room temperature for approximately 12 hours. (The speed of this reaction can be
increased by using very thin strips of egg white and/or incubating at 30°C. Students might want
to compare the action of papain or bromelin under similar conditions.)
5. Examine tubes for the presence of the egg white.

Results
After 12 hours, the egg white will be “digested” in tube B; little, if any, of the cube will remain, while
there appears to be little change in the other tubes. If allowed to incubate longer, the cube in tube D
and possibly C will decrease in size.